Mastering SQL Queries: Accessing Multiple Tables with Ease

I’ve often encountered scenarios where data is spread across multiple tables, making it challenging to retrieve the required information.

I’ll share about how to write SQL queries that access more than one table, including composing queries with nested statements, building queries with multiple tables in the FROM clause, and using implicit join queries with join criteria specified in the WHERE clause.

Accessing Multiple Tables with a Simple SELECT Statement

One of the most basic ways to query multiple tables is by using a simple SELECT statement. You can call more than one table in the statement’s FROM clause to combine results from multiple tables. Here’s an example:

SELECT table1.column1, table2.column2 
FROM table1, table2 
WHERE table1.column1 = table2.column1;

In this example, we’re using the dot notation to separate the table and column names. If the column appears only in one of the referenced tables, you don’t need to include the fully qualified name, but it’s often useful to do so for readability.

Using Nested Statements in the WHERE Clause

Sometimes, you need to access multiple tables using a nested statement in the WHERE clause. This can be achieved by using a subquery or a subselect statement. Here’s an example:

SELECT column1 
FROM table1 
WHERE EXISTS ( 
  SELECT column1 
  FROM table2 
  WHERE table1.column1 =…